The amount of carbon dioxide in the atmosphere has increased by 25% over the past 200 years. This has coincided with global industrialisation and increased use of fossil fuels. The amount of carbon (as carbon dioxide) in the atmosphere is now increasing by 4 billion tonnes a year.

The Earth's surface is heated by radiation from the Sun. Carbon dioxide and other gases in the air trap this heat radiation and prevent much of it escaping into space. The greater the amount of carbon dioxide and other heat-trapping gases, the larger is the amount of heat that is trapped and the hotter the Earth becomes. This temperature rise is called global warming.

There are several consequences of global warming:

Sea water will expand and sea levels will rise, causing flooding of low-lying land. A rise of 20 cm is predicted by 2050.

If the temperature keeps rising, the polar ice caps will melt and sea levels could rise by 20 m. This is not expected to happen for at least another century, but there are already signs of Antartic ice melting. If the ice caps melt, some flat low altitude countries such as the Maldives could disappear.

There will be big changes in global climate. Equatorial countries such as Singapore will probably experience more rain, but other countries in North America and Europe will probably suffer drought. This would result in serious food shortages.

What can be done to prevent global warming? The only practical plan at present is to reduce the amount of carbon dioxide being put in the atmosphere. This can only be done by reducing the use of fossil fuels and using other energy sources. More electricity could be generated using wind, tidal and hydroelectric power. Hydrogen, produced using solar energy, could be used as a substitute for hydrocarbons fuels in vehicles. Greater use could be made of electric vehicles.

Reducing carbon dioxide requires international agreement. There is no point in one country reducing carbon dioxide emissions on its own as a movement of atmospheric carbon dioxide does not stop at international borders. The first such agreement was made in 1999, when 38 industrialised countries agreed to cut their 'greenhouse gas' emissions to 5% below 1990 levels by 2012.

Developing nations are not bound by this agreement as fossil fuels are at present the only convenient and cheap large-scale source of energy. Limiting their use would be expensive and may retard development of poorer countries. Do we have other alternatives?